(1) Field of the Invention
The present invention relates to an image frequency restoration system for a single CCD (Charge Coupled Device) video camera, more particularly, an image frequency restoration system in digital video camera for converting an optical signal to an electrical signal using a single CCD, which may process a signal detected by a single CCD, identify the degraded factors resulting from the procedure of converting the electrical signal to a luminance signal and color signals, compensate the signals for errors, and restore the signals to the original states.
(2) Description of the Prior Art
A CCD(Charge Coupled Device) is an image pickup device which converts an optical signal into an electric charge and outputs the electric signal. A broadcast camera generally processes individual RGB e(Red.Green.Blue) signals of an image signal with three CCDs; however, a home video camera processes a RGB signal with a single CCD controlled by time division multiplexing.
A conventional single CCD color video camera will be described with reference to the accompanying drawings.
Referring to FIG. 1, the conventional single CCD digital video camera comprises a camera part 10 which receives an optical signal from a lens module and generates a television signal; a VCR(Video Cassette Recorder) part 80 which receives and stores the television signal from the camera 10; and a television part 90 which receives and outputs the television signal to an eye view finder.
In the camera part 10, an optical signal collected by a lens module 1 passes through an optical low pass filter 2 and a color filter array 3 and is converted into an electrical signal by a single CCD module 4. In the correlated double sampling and automatic gain control module 5, the noise of the electric signal is eliminated, the gain of the signal is properly controlled depending on luminance, and the signal is outputted, in analog form with gamma correction of the signal distortion. Then, the analog to digital converter 6 converts an analog signal into a digital signal, and the digital camera signal processing module 7 generates a luminance signal and a color difference signal by digital signal processing. The luminance signal and a color difference signal are converted into digital signals by digital to analog converter 8. The multiplexer 9 generates a television signal by synthesizing the digital signals.
In the digital camera signal processing module 7 as shown in FIG. 2, generating the luminance signal Y and the color difference signal C is as follows.
The detection module 11 detects the signal from the analog to digital converter 6. The color processing module 12 then processes the signal which is composed of Cyan, Magenta, Yellow and Green components, and generates the luminance signal and the RGB signals. The color difference signal generator module 13 generates the color difference signal using the RGB signals, and the encoding module 14 encodes the luminance signal and the color difference signal. Also, timing and sync signal generation module 15 generates a sync signal which synchronizes the optical low pass filter 2, the color filter array 3, CCD module 4, the correlated double sampling and automatic gain control module 5 and the multiplexer 9.
Now, the detailed operation of color processing module 12 is as follows.
The inputted color component corresponding to the color filter array in FIG. 3 is divided into an even field and odd field component, and represents RGB components in a pixel position as shown in FIG. 5.
Two different color components represented as S1 and S2 are alternatively repeated in each line, as shown in FIG. 3, FIG. 4 and FIG. 5. The procedure for extracting the RGB components from S1 and S2 components is as follows.
For all odd and even lines, the low frequency component of the luminance signal is obtained by adding S1 to S2, as shown in Eq. (1). Eq. (2) is obtained by substituting each component in Eq. (1), and Eq. (3) is obtained by sorting Eq. (2). ##EQU1##
Accordingly, the low frequency component of the luminance signal(Yl) is obtained, as shown in Eq. (4). The Yl refers to low frequency component of the luminance signal, since its composition rate is similar to that of the luminance signal Y and it passes through the planar low pass filter.
Also, the difference between S2 and S1 differs for each line. In the case of the odd field, Eq. (5), (6) and (7) are obtained. ##EQU2##
Therefore, the Cr component is obtained in the odd line of the odd field. The value of the Cr component resides between -256 and 255, and is represented in nine bits.
Similarly, Eq. (8), (9) and (10) are obtained for the even line of the even field. ##EQU3##
The value of the Cb component also resides between -256 and 255, and is represented in nine bits.
Eq. (11) to (13) are used herein among several types of the RGB matrix. EQU RED=Cr+0.2G=2R (11) EQU GREEN=Yl-Cr'=5G (12) EQU Blue=-Cb+0.2G=2B (13)
FIG. 5 illustrates the composition of the RGB signal passed through the color filter array module in FIG. 3. FIG. 6 illustrates the recomposed odd field resulted from the new type of the color filter module in FIG. 4.
Referring to FIG. 6, the Yl component of the (i, j)th pixel of the odd field is calculated in Eq. (14) using Eq. (4). EQU Yl(i,j)=S1(i,j)+S2(i,j) (14)
The Cr component in the odd line of the odd field is the difference between S2 and S1, calculated differently in the odd column and the even column.
Eq. (15) is obtained by using Eq. (7) for representing the Cr component of the odd column. EQU Cr(i,j)=S2(i,j+1)-S1(i,j) (15)
Eq. (16) is obtained by using Eq. (7) for representing the Cr component of the even column. EQU Cr(i,j+1)=S2(i,j+1)-S1(i,j+2) (16)
The Cb component in the even line of the odd field differs between the odd column and the even column. The Cb component of the odd column is presented in Eq. (17) and the Cb component of the even column is presented in Eq. (18) using Eq. (10). EQU Cb(i+1,j)=S2(i+1,j+1)-S1(i+1,j) (17) EQU Cb(i+1,j+1)=S2(i+1,j+1)-S1(i+1,j+2) (18)
Since there is no Cr component in the even line and no Cb component in the odd line, the Cr component used in the even line is that of the Cr component of the preceding line and the Cb component used in the odd line is that of the Cb component of the following line, as shown in Eq. (19) and (20). EQU Cr(i+1,j)=Cr(i,j) (19) EQU Cb(i,j)=Cb(i+1,j) (20)
The resultant RGB signals are obtained by substituting Yl, Cr and Cb components from Eq. (11) to (13).
For the odd field as shown in FIG. 4, the components are different depending on the odd column of the odd line, the even column of the odd line, the odd column of the even line and the even column of the even line, i.e., the composition of the components are repeated as shown in FIG. (7).
Therefore, the impulse response is obtained from processing four pixel positions of (1,1), (1,2), (2,1) and (2,2).
Now, the Yl, Cr and Cb components of the odd field are as follows.
Eq. (21) to (24) below represent the Yl component of the odd field. EQU Yl(1,1)=S1(1,1)+S2(1,2) (21) EQU Yl(1,2)=S1(1,2)+S2(1,3) (22) EQU Yl(2,1)=S1(2,1)+S2(2,2) (23) EQU Yl(2,2)=S1(2,2)+S2(2,3) (24)
Also, Eq. (25) to (28) below represent the Cr component of the odd field, and Eq. (29) to (32) below represent the Cb component of the odd field. EQU Cr(1,1)=S2(1,2)-S1(1,1) (25) EQU Cr(1,2)=S2(1,2)-S1(1,3) (26) EQU Cr(2,1)=S2(1,2)-S1(1,1) (27) EQU Cr(2,2)=S2(1,2)-S1(1,3) (28) EQU Cb(1,1)=S2(2,2)-S1(2,1) (29) EQU Cb(1,2)=S2(2,2)-S1(2,3) (30) EQU Cb(2,1)=S2(2,2)-S1(2,1) (31) EQU Cb(2,2)=S2(2,2)-S1(2,3) (32)
Eq. (33) to (44) represent the recomposed G' components of the odd field, Eq. (45) to (53) represent the recomposed R' components of the odd field and Eq. (54) to (65) represent the recomposed B' components of the odd field. ##EQU4##
The recomposed R', G' and B' component signals should be recomposed in the signal shape of the field unit since they are composed of frame units, as shown above. FIG. 8 illustrates the method of recomposing the signals in field units.
The method of recomposing in FIG. 8 is as follows.
Eq. (66) to (99) represent the recomposed R" components of the odd field, Eq. (70) to (73) represent the recomposed G' components of the odd field and Eq. (74) to (77) represent the recomposed B" components of the odd field. ##EQU5##
From the above Eq. (66) to (77), since the R", G" and B" components of the odd field of the signal from the color processing module 12 are degraded with channel correlations, it is difficult to realize the original color component of the signal.